1. Field of the Invention
The present invention relates to a variable delivery fuel supply device which is used for an internal combustion engine for automobiles, in particular, for a cylinder injection type gasoline engine requiring highly pressurized fuel and which is capable of controlling an amount of fuel to be supplied to fuel injection valves.
2. Discussion of Background
FIG. 4 is a systematic diagram showing the construction of a conventional variable delivery fuel supply device, wherein reference numerals 1a through id designate fuel injection valves for injecting fuel into respective cylinders of an internal combustion engine, numeral 2 designates a delivery pipe for supplying fuel to the fuel injection valves 1a-1d, numeral 3 a fuel pump for supplying pressurized fuel to the delivery pipe 2, numeral 4 a low pressure fuel pump for supplying fuel from a fuel tank 5 to the fuel pump 3, numeral 6 a check valve provided in a fuel passage 7, numeral 8 a low pressure regulator for controlling pressure in the fuel passage 7, numeral 9 a relief valve for relieving fuel from a fuel passage 10 through a fuel passage 11 to the fuel tank 5 when a fuel pressure in the delivery pipe 2 exceeds a predetermined value, and numeral 12 a return passage for returning fuel through the fuel pump 3 to the fuel tank 5.
The fuel pump 3 comprises a cylinder, a plunger performing a reciprocating movement in the cylinder due to a driving action of a cam provided on a cam shaft of the internal combustion engine and a pressurizing chamber for sucking fuel during the reciprocating movement of the plunger to pressurize the fuel, although these structural components are not shown in the drawing. The fuel pump 3 is to receive fuel supplied from the fuel tank 5 through a fuel intake port 13; to feed the fuel into the pressurizing chamber via a fuel passage 14 and an intake valve 15 in a suction step; to supply forcibly the fuel pressurized in the pressurizing chamber to a discharge port 18 via a discharge valve 16 and a fuel pressure maintaining valve 17 in a discharge step; and to supply the fuel to the delivery pipe 2 through the fuel passage 10 whereby the fuel in the delivery pipe 2 is distributed to the respective fuel injection valves 1a-1d. 
Reference numeral 19 designates an electromagnetic valve disposed in the fuel pump 3, which is to open and close a relief passage 20 for communicating the pressurizing chamber (not shown) in the fuel pump 3 with the fuel passage 14. When control means (not shown) detect that a fuel pressure in the delivery pipe 2 reaches a predetermined value, the control means supply a valve-opening signal to the electromagnetic valve 19. Then, the electromagnetic valve 19 is opened to communicate the pressurizing chamber, in which a highly pressurized fuel is stored, with the fuel passage 14 of low fuel pressure to thereby relieve the pressurized fuel. Thus, the fuel pressure in the delivery pipe 2 can be controlled by controlling an amount of fuel discharged from the fuel pump 3. The fuel pressure of the delivery pipe 2 increases since fuel is supplied in a discharge step of the plunger of the fuel pump 3. Accordingly, the valve-opening operation of the electromagnetic valve 19 is conducted in the discharge step.
In the conventional variable delivery fuel supply device having the above-mentioned structure, the discharge performance of the fuel pump 3 is so determined as to cover the fuel consumption rate of the internal combustion engine over the entire operational range. Accordingly, there is allowance in the discharge performance of the fuel pump in a normal state of operation, and the electromagnetic valve 19 is opened at every discharge step whereby the highly pressurized fuel flows in a pulse form in the fuel passage 14. The pulsating flow of the pressurized fuel generates a pulse-like fuel pressure in the fuel passage 14 and the fuel passage 7 as supply passages for fuel of low pressure. The amplitude of a pressure pulsation will increase as a rotating speed of the internal combustion engine is increased, with the result that vibrations are generated in a fuel pipe such as the fuel passage 7 whereby noises are generated and damage is caused in the fuel pipe due to a mechanical stress by the vibrations. Further, the pressure pulsation creates a disturbance flow or cavitation in the passage for supplying fuel of low pressure, which may cause an unstable supply of fuel to the delivery pipe 2 and influences adversely the performance of the internal combustion engine.